A detailed study of the effects upon the thermodynamic stability of both human and bovine serum albumin resulting from: a) the method of purification, b) incubation at 60 degrees C, c) ligand binding at the fatty acid and aromatic binding site(s) has been carried out by differential scanning calorimetry. Enthalpic and entropic contributions to the protein stability have been evaluated. The major structural protein of the bacteriophage T4 capsid, gp 23, self-assembles into various microtubular "polyhead" structures. The thermodynamic parameters associated with the conversion of the "expanded" lattice polyhead to denatured monomeric cleaved protein, gp 23*, has been determined by differential scanning calorimetry.